Several methods for the decaffeination of tea are known, dealing in part with the manufacture of caffeine free tea leaves, and in part with the manufacture of caffeine free, soluble tea extract powders. In contrast to the decaffeination of coffee, which occurs almost exclusively in the raw beans, the decaffeination of tea must be accomplished, in areas where the tea plant is not grown, on a dried and fermented product which, in addition, is also extremely sensitive with respect to its aroma. It is significant that only a few manufacturers offer caffeine free tea. One of the reasons is primarily the aroma problem which cannot be solved satisfactorily with any of the previously known methods.
For example, a decaffeination procedure is described in Swiss Pat. No. 164,535 in which an aqueous tea extract free of caffeine was produced by means of percolation with a caffeine-solvent immiscible with water, after which the previously extracted tea was impregnated with the now caffeine free, concentrated extract and subsequently dried. The aqueous tea extract was made slightly ammoniacal in order to prevent precipitation from separating.
In another method (German Pat. No. 196,835) the aromatic substances were first removed from the tea by means of petroleum ether. The tea was then moistened, ammonia was conducted through it to crack the caffeine-complex salts, and the caffeine was subsequently extracted with solvents. After drying the tea, the aromatic substances which were initially removed from it with the petroleum ether were again added to the tea.
A similar method is described in the French Pat. No. 791,055 in which the aromatic substances are extracted by means of a solvent having a low boiling point, such as dichlorethylene, the extraction of the caffeine being accomplished by a solvent having a higher boiling point, such as carbon tetrachloride, after a treatment with alcoholic ammonia solution. In another variation of the method, the aromatic substances and the caffeine are removed from the tea at the same time by a solvent mixture and, after fractionating the extract, the aromatic substances are reincorporated into the tea.
In another method (German Disclosure No. 1,807,308) an aqueous tea extract is produced after removing the caffeine with organic solvents. Since aromatic ingredients also dissolve in this process, they are recovered separately from the organic solvents and subsequently added to the decaffeinated tea extract. The result is an instant tea.
All of the previously known methods have several drawbacks. Either one has to work, among others, with ammonia or sulfur dioxide in a doubtful manner with respect to the food laws to crack the caffeine-complex salts in the tea leaf, for instance; or the aromatic substances must be recovered from a solvent fraction, in which process it is generally not possible, due to the nature of the usually oily aromatic ingredients, to remove all solvent residues from them completely; or, where this is accomplished, it is associated with a considerable less, in particular of the volatile aromatics.
The objective of the present invention is a method for the manufacture of caffeine free black tea leaves as well as of caffeine free instant tea, while avoiding the disadvantages of the hitherto known methods.